From ff236897195c8e927268e51ea469dbf46591e75f Mon Sep 17 00:00:00 2001
From: Andrew Lorimer <andrew@lorimer.id.au>
Date: Tue, 26 Mar 2019 22:22:26 +1100
Subject: [PATCH] [chem] equilibrium constant and qualitative stoichiometry

---
 chem/prac-9-aim.md |  5 ++++-
 chem/reactions.md  | 44 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/chem/prac-9-aim.md b/chem/prac-9-aim.md
index e16b2e9..ebcff8d 100644
--- a/chem/prac-9-aim.md
+++ b/chem/prac-9-aim.md
@@ -1,3 +1,6 @@
 # Experiment 9 - Effect of temperature and pressure on equilibrium
 
-To determine the effect of the temperature and pressure of an equilirium environment on the direction of the equilibrium reaction. Temperature is tested by adding methyl violet indicator to a solution of phosphoric acid which shows the concentration of ionised H+ and H2PO4- ions. Pressure (inversely proportional to volume) is tested with dinitrogen tetroxide and the colour change is observed. 
+To determine the effect of the temperature and pressure of an equilirium environment on the direction of the equilibrium reaction. Temperature is tested by adding methyl violet indicator to a solution of phosphoric acid which shows the concentration of ionised H+ and H2PO4- ions. Pressure (inversely proportional to volume) is tested with dinitrogen tetroxide and the colour change is observed.
+
+N2O4(g) <-> 2NO2(g)
+  clear <-> brown
diff --git a/chem/reactions.md b/chem/reactions.md
index f3c9800..7e8d080 100644
--- a/chem/reactions.md
+++ b/chem/reactions.md
@@ -40,3 +40,47 @@ Haber process (ammonia producition) - enzymes are catalysts for one reaction eac
 
 **Equilibrium** - the stage at which quantities of reactants and products remain unchanged  
 Reaction graphs - exponential/logarithmic curves for reaction rates with time (simultaneous curves forward/back)
+
+## Equilirbium constant $K_C$
+
+For reaction $aA + bB + cC + dD + \dots \leftrightarrow zZ + yY + xX + \dots$:
+
+$$K_c = {{[Z]^z [Y]^y [X]^x \dots} \over {[A]^a [B]^b [C]^c [D]^d \dots}}$$
+
+Indicates extent of reaction. If value is high ($> 10^4$), then [products] > [reactants]. If value is low ($< 10^4$), then [reactants] > [products].
+
+If $K_c$ is small, equilibrium lies *to the left*.
+
+**$K_c$ depends on direction that equation is written (L->R)**
+
+## Reaction constant $Q$
+
+Same for as $K_C$. If $Q=K_c$, then reaction is at equilibrium.
+
+## Le Châtelier’s principle
+
+> Any change that affects the position of an equilibrium causes that equilibrium to shift, if possible, in such a way as to partially oppose the effect of that change.
+
+### Changing volume
+
+1. $\Delta V \implies [\Sigma \text{particles}] \uparrow$, therefore system reacts in direction that produces less particles
+2. $\Delta V \implies [\Sigma \text{particles}] \uparrow$, therefore system reacts in direction that produces more particles
+2. $n(\text{left}) = n(\text{right})$ (volume change does not disturb equilibrium)
+
+### Changing temperature
+
+Only method that alters $K_c$.
+
+Changing temperature changes kinetic energy. System's response depends on whether reaction is exothermic or endothermic.
+
+- Exothermic - increase in temperature decreases $K_c$
+- Endothermic - increase in temperature increases $K_c$
+
+Time-concentration graph: smooth change
+
+## Yield
+
+$$\text{yield %} = {{text{actual mass obtained} \over {theoretical maximum mass}} \times 100$$
+
+
+
-- 
2.43.2